Why is pre-heating important?
The first roast of the day is always the most difficult in coffee roasting. Virtually every roaster I've come across has an issue getting their first roast to be consistent with their subsequent batches. Some roasters even intentionally throw away their first batch of the day or allocate it for "less important" coffees like decaf or cold brew. What a waste!
It doesn't have to be this way. There are effective ways of pre-heating the coffee roaster that can yield great results and provide a great first roast that is consistent with your subsequent batches. Let's look at the main idea behind pre-heating now.
The concept of pre-heating
There are two key objectives when it comes to pre-heating the coffee roaster.
1. The first is objective is the thermal energy stored within the coffee roaster. This is a result of the heat input from the burners and the length of time of the pre-heating routine. Of course, other factors like the ambient temperature, humidity, airflow within the roaster and drum speed will have an impact on the roaster's rate of storing thermal energy during the pre-heating phase.
2. The second objective is ensuring the thermal energy is evenly spread out within the roaster. It wouldn't do us much good if different parts of the roaster are heated up to different thermal states. It would result in an equally uneven roast. This is easy enough to achieve by ensuring sufficient airflow through the roaster during the pre-heating routine. Do not close off or reduce airflow to a minimum. You want a medium to strong airflow during this phase to help evenly heat up the roaster (Not to the point where the heat is being drawn out of the roaster, that would be too much and an inefficient use of the heat energy.)
Examples of roaster's warmup routines
1. Allowing the roaster's burner to idle at a fixed gas % for x amount of time.
2. Bringing the roaster to x temperature using maximum gas. Subsequently adjust the gas % to allow it to idle at that temperature for y amount of time.
3. Bringing the roaster to x temperature using a fixed % gas setting.
4. Bringing the roaster to x temperature, flush out the heat using high airflow then return airflow to normal to allow it to return back to the same temperature. Repeat flushing y number of times.
Does your pre-heating routine resemble any of the above? Let us know how you like to pre-heat your roaster in the comments section below! Maybe even try the above and see how they work out for you.
Pre-heating best practices
As mentioned earlier, the ambient conditions can have an effect on the heating up of the coffee roaster. It is good practice to record these elements such as the ambient humidity, temperature and atmospheric pressure to see the effect they have on your pre-heating.
Another great practice as recommended by one of our roasting coaches, Ben Toovey, is to keep a roast curve of your warming up routine. That way, you have a reference curve that you can compare to see if you are warming up slower or faster than usual. This is especially helpful in countries with different seasons as they have a dramatic impact on the roaster's thermal energy.
Ben covers pre-heating and much more in his masterclass on quality control and roasting operations best practices. Learn more about his class in the Ultimate Coffee Roasting Course today!
Our method of pre-heating
We've come up with our own method of pre-heating. As mentioned in the video above, there are numerous variables to track to assess the thermal energy in the roaster.
The explanation might be a bit complicated so here's a quick summary.
Pre-heating to a specific BT/ET, with the Airflow, Drumspeed and Gas pressure kept to a fixed setting. Once you hit your specified BT/ET, you want your idling ROR to be the same every time you pre-heat your roaster. Comparing to your reference curve, If ROR is slower than normal= too cold. ROR is faster than normal = too hot.
So what's the best way to pre-heat your coffee roaster?
Pre-heating routines isn't a one size fits all and there are multiple routines that could work. What's important is to understand which variables to track and keep consistent in order to ensure optimal results with your own roaster.
Want to learn more about the 15 variables that impact coffee roasting? Check out our Ultimate Coffee Roasting Course! You'll get access to all our secrets, knowledge and experience in coffee roasting and even masterclasses from roasting champions around the world!
And if you have any coffee questions you'd like us to answer, leave them in the comments section below and we'll make sure to answer them in future posts.